(Invited) Status and Future Perspectives of Redox Flow Batteries

Abstract

The trends of growing renewable penetration and demand of reliable, flexible, clean and affordable electricity have driven ever increasing interests of electrical energy storage (EES). Applications of EES as utility assets have seen significant growth around the globe in the past few years. Among varied EES technologies, batteries that convert chemical energy into electricity or vice versa offer quick response and unparalleled flexibility and have thus been one of the most developed and commercialized. Particularly, redox flow batteries (RFB’) have been among the leader in emerging battery technologies for utilities, independent power producer, microgrid, and commercial and industrial customers. Unlike other battery chemistries, such as lead-acid and Li-ion or generally classified as solid-state batteries, RFB’ were developed specifically for utility applications. With energy stored in liquid electrolytes and without ionic diffusion in the solid electrodes, these batteries work in a unique way that enables a set of unique advantages over the solid-state batteries. These may include separated design of energy (kWh) and power kW), a superior cyclability, a long life and full access to rate capacities over the life. More importantly, the RFB so far, including vanadium RFB’ or VRFB’, Zn-halide, etc., most use aqueous electrolytes and are inherent safe. The unique advantages, along with the performance flexibility demonstrated allow for stacking benefits for a safe EES solutions of a maximized value to customers. As emerging technologies, however, RFB’ have found a limited share in the early market that has been dominated by Li-ion batteries lately. Though there have been many deployments in the fields, the RFB’ are still being optimized to achieve a full maturity and have not yet produced at scales. Pressure is also on to reduce costs and make competitive in the markets. This paper will review progress and challenges of the redox flow battery industry and technology development and share perspectives in future directions.